The present invention relates to a method for regulating the polymerization of cyclic polycarbonates using a polymerization initiator and a phenol or polyphenol as a chain-transfer agent. More particularly, the present invention relates to a method for making hydroxyl-terminated polycarbonate oligomers of a predetermined molecular weight.
As used hereafter, the term cyclic polycarbonate, polycarbonate, or cyclic polycarbonate oligomer means cyclics or polymers made from the reaction of bisphenols, such as bisphenol-A with phosgene.
Prior to the present invention, one method of regulating the molecular weight of polycarbonates involved the employment of a diarylcarbonate as a chain-transfer agent.
Although diarylcarbonate has been found to be an effective chain-transfer agent, the polycarbonate chains made by this procedure are capped with arylcarbonate end-groups. It would be desirable, therefore, to provide a method for polymerizing cyclic carbonate with a chain-transfer agent which would result in hydroxyl-terminated polycarbonate oligomers as well as offer greater potential for making copolymers, as well as provide cross-linking of polycarbonates during polymerization.
The present invention is based on the discovery that phenols, including polyhydric phenols, can be used effectively as chain-transfer agents for the polymerization of cyclic carbonate if used in combination with an effective amount of a polymerization initiator. There can be obtained hydroxyl-terminated polycarbonate oligomer having a predetermined block size which can be made under solution blending or melt polymerization conditions.